Onan Quiet Diesel 7500 - new fuel pump not working

[SoCalD]

I have an Onan Quiet Diesel 7500 HDKAJ spec F. I recently changed the fuel pump and the fuel filter because the generator would shut off while driving and would be hard to restart. Once I changed both, it would start right up and run great. This worked for about 4 times. The 5th time I tried to start the generator, I did not hear the clicking sound of the fuel pump priming when I hit the start button. I held the stop button down to try and run the prime function only and did not hear the pump running either. Is it possible that my new fuel pump already failed? Do you think my my wire connections came loose? The only other clue I can mention is when I installed the new fuel pump, I forgot to put the little black donut or "air seal" Onan calls it that fits around the end of the pump. Not sure if that would cause anything but maybe the air rushing out of the hole there was making the pump wires flap around and became disconnected?

[jacwjames]

Why did you change the old pump?


I would check the connections just to confirm there are not issues with the wiring.

On my 7500 there is an access cover on the panel where you start it. There a 3 fuses under the panel, one is for the start circuit which may also include the fuel pump.

[dmctlc]

Originally Posted by SoCalD

I have an Onan Quiet Diesel 7500 HDKAJ spec F. I recently changed the fuel pump and the fuel filter because the generator would shut off while driving and would be hard to restart. Once I changed both, it would start right up and run great. This worked for about 4 times. The 5th time I tried to start the generator, I did not hear the clicking sound of the fuel pump priming when I hit the start button. I held the stop button down to try and run the prime function only and did not hear the pump running either. Is it possible that my new fuel pump already failed? Do you think my my wire connections came loose? The only other clue I can mention is when I installed the new fuel pump, I forgot to put the little black donut or "air seal" Onan calls it that fits around the end of the pump. Not sure if that would cause anything but maybe the air rushing out of the hole there was making the pump wires flap around and became disconnected?

So I don't mean to hi-jack your thread but ironically I'm having issues similar to what your having after your changed out your fuel pump. Though I changed nothing it just started happening the other day when I went to do my monthly startup and running with a load. I have a Cummins/Onan ^,000 watt Model 6HDKAH-1044N Spec: N. The Generator has 220 hrs. on it and though my DP is a 2018 the original owners bought it in in May 2019 put about 8,000 on it and about 190 Hrs. on the generator so I guess they were either boondocking a lot or had it running continually while they were traveling. I bought it when they moved up to a larger DP in May 2020. I've already learned from this thread about the fuses which I missed when I was checking things out. I already pulled off and cleaned both + & - power cables and no change so I'll check the fuses today. I'll be watching this thread. I was wondering, being unfamiliar with Diesel engines, where the started would be on this unit. To me it sounds like the clicking noise is the starter not engaging though getting power but of course that's what it sounds like on a gas engine not sure if it's different. thanks

[vito.a]

Usually they use a small square Fass electric fuel pump like this:
https://www.amazon.com/UTSAUTO-Elect...%2C238&sr=8-29
They do occasionally fail. They are inexpensive enough to order a spare and try it.

[Mile Marker 42]

Would for sure make sure all fuses are correct as well as the battery used to start the gennie. I have a 7500 quiet diesel with 757 hours of use on a 2003 Monaco. All from previous owner. My hours are only "exercise" hours as everywhere we go we get full hookups. However, 2 months ago when I went to "exercise" my gennie, it would start, shut off, start run for 10 mins and shut off. This went on for 3 or 4 more times. Usually, it would take my gennie 2 times to start and stay running, so this was strange. I checked for a code and I believe it was code 25 or whatever the coolant sensor code is that was showing. To replace that $20+- part, the whole generator has to come out the front of the motorhome. I came here asking if anyone had any magic tricks or whatever. Someone replied who is in the aviation business, suggested I remove both positive and negative cables from the generator for 20-30 mins and wire brush their terminals and cable ends. I did this, and then held the start button down for 60 seconds, then started the gennie and it has been perfect since. Just went to exercise it over the weekend and let it run for 30mins with hot water heater on and off. Started first time and rant he entire 30 mins. This might work for you???

[SoCalD]

Originally Posted by jacwjames

Why did you change the old pump?


I would check the connections just to confirm there are not issues with the wiring.

On my 7500 there is an access cover on the panel where you start it. There a 3 fuses under the panel, one is for the start circuit which may also include the fuel pump.

Changed the old pump because the original symptoms I was having (engine shutting off after a short time) before this new problem pointed to either a bad fuel filter or pump. So since fuel pumps are cheap and was in there replacing the fuel filter already, I said why not change the pump. And it worked, generator did not shut off anymore. Will check the connections, I did check the fuses and they look fine. I don't think any of the fuses are dedicated to the fuel pump. The closes one is likely the one for the control board but that fuse is working since I can get the start button to work.

[USMCRET]

What code is thrown when it shuts down without being told to?

[Mile Marker 42]

There is a method to access that and I forgot. Holding down the button and then pressing a few times. Google it, you'll find it.

[bpu699]

You sure it’s not bad fuel, clogged filter, junk in the fuel pump?

[SoCalD]

Originally Posted by USMCRET

What code is thrown when it shuts down without being told to?

I used to have code 36 before I I changed the fuel pump. Now that I cannot get the generator started at all there are no codes.

[firedoc]

Or bad batteries....

Had same type of failure. Long story short. Found house batteries were bad, replaced house batteries and , voila, no problems. You could check the output of your batteries under stress and the voltage deliver to starter of gen. Needs to be 13v +-

[Mile Marker 42]

Can you confirm you have 12 volts to the generator?

[SoCalD]

Originally Posted by firedoc

Or bad batteries....

Had same type of failure. Long story short. Found house batteries were bad, replaced house batteries and , voila, no problems. You could check the output of your batteries under stress and the voltage deliver to starter of gen. Needs to be 13v +-

Interesting. I thought that start batteries for the main engine is what powered the genset control board and engaged the starter. So it is the house batteries?

[jelag]

I think you have a loose fitting on the suction side of the fuel pump and are pulling some air into the line and filter.... with any air in the line you will fail to start....


Pull the line off the OUTPUT side of the filter.... attach a rubber hose and put the hose into a jar with some fuel in the bottom.... push the button to prime... and see if there are air bubbles coming through the line... air bubbles means its drawing air and won't run....


BTW you understand that there are usually 2 draw down lines on the tank.... one to the gen set and the other the engine.... once the tank gets below about 3/8 of a tank, the gen set runs out of fuel and it pumps air and not fuel so that you can't start the engine and get to fuel....



Thus the prime feature.... to prime past all that air.... I've personally learned that if you change the filter you need to really run the prime function and purge all the air to get the gen set to start and stay running and any air will cause low fuel pressure and it will stop....